KABUL (AFP) ― He was only on the ground for 48 hours, but America’s top diplomat John Kerry may well have helped prevent Afghanistan from sliding into another bloody ethnic war.

The helicopters were waiting for the U.S. Secretary of State when he arrived in Kabul from Beijing early Friday on a last-minute mission to broker an end to a tense political impasse.

Some 48 hours later they flew him back over the darkened city streets from the fortress-like U.S. embassy compound to his plane ― a deal triumphantly in his hand.

Few had believed it possible that Kerry could bring together two presidential rivals bitterly at odds over disputed elections, and help avert fears of ethnic violence in a country ravaged by decades of war.

But the indefatigable 70-year-old dropped a political bombshell when he announced that rivals Abdullah Abdullah and Ashraf Ghani had agreed that every one of the eight million votes cast in their June run-off poll would be audited.

Just days earlier the two men were barely speaking, as Abdullah vehemently accused Ghani of stealing victory by stuffing the ballots.

But standing next to each other with Kerry late on Saturday before the world’s cameras, they clasped hands, smiling, and raised them in the air.

With that single dramatic show of unity, Kerry may well have helped guide Afghanistan’s young democracy away from a return to the bloody ethnic civil war of the 1990s.

The announcement followed two days of marathon meetings, with Kerry and his staff shuttling between the two candidates and their teams in the embassy.

He also met for hours one-on-one with each candidate.

With Kerry due in Austria for talks on a Iran nuclear agreement, Saturday’s window for a deal was closing rapidly.

“It wasn’t until the 11th hour ... that we had a full agreement,” a senior U.S. official who took part in the negotiations told journalists.

The talks had focused on the best mechanism for auditing the poll results.

A second track sought to persuade the feuding rivals to meet to discuss their differences and clear the way towards a national unity government.

Afghan analyst Younus Fakour said the agreement had “prevented a disaster in Afghanistan, it prevented the creation of a parallel government, it prevented chaos” ― and the national unity government element was crucial.